This invention relates to a variable magnification type copying machine with a zoom lens. More particularly, it relates to a focus and magnification determining and control device which provides proper focus and magnification irrespective of temperature variations and component deterioration.
In variable magnification copying machines with a zoom lens, magnification is changed by moving the movable lenses of the zoom lens. Any variations in the distance between the objject on the machine platen and the image receiving photosensitive surface is compensated for by adjusting the distance between the movable lenses by means of a cam or the like. However, in the conventional copying machine, the positions of the movable lenses of the zoom lens relative to the platen and photo sensitive surface and the distances between the movable lenses themselves are predetermined according to optical calculation values which correspond to given copying magnifications for given component values and operating conditions. Therefore, should there be temperature changes or changes in component parameters due to deterioration, manufacturing variations, or the like, incorrect focus and magnification result. Such incorrect focuses and magnification settings give rise to inferior picture quality. Thus, it was necessary to manufacture copying machine components with a high degree of accuracy, and accordingly, the conventional copying machine has an unavoidably high manufacturing cost.